1. Field of the Invention
The invention relates to an apparatus for the proportioned feeding of an analysis fluid onto a target, in which the fluid is ejected onto the target in small quanta pulse-wise out of a nozzle through a nozzle outlet opening.
In clinical chemistry it is often necessary to apply an analysis fluid onto a target in exact quantity. The fluid may be for example a reagent fluid, a calibration fluid or a sample fluid, in particular blood or serum.
The target to which the fluid is to be fed may be a reaction vessel, for example in an automatic analysis unit. Other examples are the microtitre plates frequently used in microbiology and the solid phase analysis elements in very common use today, which are also described as "test carriers" and, in the Anglo-Saxon literature, as "solid state analysis elements". For the purpose of the present invention the term "analysis elements" denotes in addition to discrete test carriers (such as e.g. test strips and analysis slides) also tapes, strips or other forms of continuous analysis elements which are directed past a proportioning station at which the analysis fluid is applied.
2. Description of the Prior Art
Use is traditionally made for the feeding of analysis fluids of various forms of piston-cylinder apparatuses, such as e.g. pipettes, dispensers and diluters. The reagents have usually been applied to analysis elements by impregnation of the reagents-carrier matrix (for example paper) or a reagent film has been produced in a layer-forming process from a fluid containing film-forming polymers. Printing techniques have also been proposed.
In EP-A-119 573 and in EP-A-268 237 (U.S. Pat. No. 4,877,745) apparatuses of the kind mentioned in the preamble are described. Their technique is based on the ink jet technology developed originally for computer printers (ink jet printers). Both documents contain more detailed explanations of the known state of the art, to which reference is made here.
These known apparatuses for the microproportioning of analysis fluids have in each case a nozzle compartment whose volume is compressed for a short time in order to eject a quantum of analysis fluid. In the case of EP-A-119 573 the nozzle compartment is formed by a section of an elastic tube, against whose lateral surface an electromagnetically moved cylindrical rod is directed, which is moved against the tube whenever a drop is to be ejected. In the case of EP-A-268 237 the nozzle compartment consists of a tubular piece which is surrounded by a coaxial piezoelectric actuating element likewise formed in a tubular shape.
The "drop on demand" printing techniques make it possible to apply extremely small volumes of analysis fluids contact-free, accurately and quickly onto a target. The extraordinarily small volume of the individual quanta, which is usually some 0.2 nl and does not exceed about 1 nl, is however disadvantageous for many applications. If larger volumes are required, hundreds or thousands of jet quanta have to be ejected one after the other. The time required is considerable despite the high injection rate. In the case of easily volatile reagent fluids there is the risk that a substantial proportion of the small droplets will evaporate. In addition the ejection of the quanta is interrupted if a gas bubble of minute size forms in the nozzle compartment in the vicinity of the nozzle outlet opening. In the case of printers the formation of such gas bubbles can be avoided by the use of special inks. In the case of analysis fluids, however, this solution is not an option.